This invention relates generally to top/bottom pincushion correction circuits and specifically to active top/bottom pincushion circuits.
As fully discussed in the copending application, the use of cathode ray tubes (CRTs) in video monitors that are driven by computers and the like has imposed stringent demands upon the shape and linearity of the generated rasters. These control demands and the desirability of achieving pincushion correction circuitry that is individually controllable for top and bottom correction are achievable wih the use of active devices in the pincushion correction signal generation circuits. In such circuits, a pincushion transformer has a secondary winding connected in series with the yoke and the vertical deflection amplifier. The transformer enables a pincushion correction current to be injected into the yoke. Difficulty can arise due to the low output impedance of the pincushion correction amplifier. Specifically, the primary winding of the pincushion transformer and the coupling capacitor connecting the transformer in the output circuit of the pincushion amplifier may resonate during occurrence of the large retrace pulse in the vertical deflection signal. The present invention provides a solution that is both simple and effective for inhibiting the ringing currents that would normally be generated.